A vehicle control system is known in the art, for example, as disclosed in Japanese Patent Publication No. 2009-29344. According to the vehicle control system (JP No. 2009-29344), a time period is increased for a coast-lock-up operation and a fuel-cut operation in order to improve fuel consumption ratio. In addition, an operation of an air-conditioning apparatus is stopped during a vehicle acceleration period.
Another vehicle control system is known in the art, for example, as disclosed in Japanese Patent Publication No. 2009-12721. According to this prior art, a cool-storage device is provided in a vehicle air-conditioning apparatus and an operation of a compressor is controlled to be switched-on or switched-off in order to achieve a sufficient effect for reducing fuel consuming amount.
According to the above prior art (JP No. 2009-12721), a heat cost (g/kwh) is calculated. The heat cost is a fuel consuming amount necessary for generating a unit amount for heat of cooling (a unit amount for cooling energy) by an operation of a refrigerating cycle. The heat cost is compared with a threshold value and the compressor is operated when the heat cost is lower than the threshold value. Refrigerant discharged from the compressor is supplied to an evaporator and a cool-storage device, so that not only a passenger compartment of the vehicle is cooled down by the evaporator but also cooling energy of the refrigerant flowing from the evaporator to the cool-storage device is stored in the cool-storage device.
On the other hand, when the heat cost is higher than the threshold value, the operation of the compressor is stopped so that the refrigerant flows from the cool-storage device to the evaporator via a bypass passage until refrigerant pressure in a condenser becomes equal to that in the cool-storage device. As a result, the evaporator is continuously operated to cool down air passing through the evaporator.
A further vehicle control system is known in the art, for example, as disclosed in Japanese Patent Publication No. 2010-30497. According to such a prior art, cooling energy is stored in a cool-storage device not only in a vehicle acceleration period but also in a vehicle deceleration period. When supply of refrigerant from a compressor to the cool-storage device is stopped in the vehicle deceleration period, a braking distance of a vehicle may be increased or discomfort may be given to a vehicle passenger because a braking torque by the compressor disappears due to stop of the compressor operation. The above prior art discloses the vehicle control system for overcoming such problems.
In the above prior art, the compressor operation is stopped in the vehicle deceleration period, when the cooling energy is fully stored in the cool-storage device and thereby it becomes impossible to further store the cooling energy in the cool-storage device. When such a situation occurs, a control signal is transmitted from a control unit of the air-conditioning apparatus to a control unit for an automatic transmission apparatus so as to increase a reduction gear ratio of a stepless-speed-change device. As a result, a portion of the vehicle decelerating torque, which is coming short due to the stop of the compressor operation, is compensated.
A still further vehicle control system is known in the art, for example, as disclosed in Japanese Patent Publication No. 2005-207321. The patent document discloses the vehicle control system, according to which cooling energy stored in a cool-storage device is effectively used. In addition, according to the vehicle control system, an engine for a vehicle and an air-conditioning apparatus are cooperatively and totally controlled.
Furthermore, according to the prior art (JP No. 2005-207321), the vehicle control system is composed of;
the cool-storage device for storing at least a portion of the cooling energy generated by the air-conditioning apparatus;
a cooling-energy amount detecting sensor for detecting a stored amount of the cooling energy in the cool-storage device;
a vehicle-condition detecting portion for detecting an environmental condition of the vehicle (such as, inside temperature, inside humidity, outside temperature, amount of solar radiation, preset temperature for the air-conditioning apparatus and son);
a cooling-energy calculating portion for calculating an amount of cooling energy necessary for cooling a passenger compartment of the vehicle based on detected information from the vehicle-condition detecting portion; and
a control portion for controlling an operating condition of the vehicle based on the stored amount of the cooling energy in the cool-storage device and the amount of the cooling energy necessary for the air-conditioning operation.
According to the above prior art (JP No. 2009-29344), the vehicle control system aims to reduce the fuel consuming amount for cooling operation by increasing discharge amount of the refrigerant from the compressor when the vehicle control system estimates the vehicle decelerating operation. Cooling efficiency (an inverse number of the heat cost) is related to not only the vehicle condition of the accelerating operation but also engine rotational speed, output torque, capacity of the compressor, flow rate of the refrigerant, refrigerant pressure and so on. Even when the discharge amount of the refrigerant is increased in the case of the estimation for the vehicle decelerating operation, the cooling efficiency of the air-conditioning apparatus may be low depending on various vehicle condition and other circumstances. Therefore, the fuel consumption ratio may be adversely affected in some of the cases.
In addition, effect for reducing the fuel consuming amount in the vehicle decelerating period by increasing the discharge amount of the refrigerant from the compressor is related to not only the cooling efficiency in the vehicle decelerating operation but also an average cooling efficiency of a whole operating period of the air-conditioning apparatus. In other words, if the discharge amount of the refrigerant is increased in the vehicle decelerating period and if the cooling efficiency during such operation is lower than the average cooling efficiency, the fuel consumption ratio may be adversely affected.
When the cool-storage device is provided, a total amount for storing the heat of cooling (the cooling energy) is increased in the air-conditioning apparatus. In such an air-conditioning apparatus, the stored cooling energy is radiated when the cooling efficiency is low, so that the fuel consuming amount can be reduced. In other words, when the air-conditioning apparatus is operated in such a way that the cooling energy is stored in the cool-storage device only in the period of the fuel-cut operation or in the vehicle decelerating operation, the effectiveness for reducing the fuel consuming amount cannot be sufficiently increased.
None of the above prior arts (JP No. 2009-12721, JP No. 2010-30497, JP No. 2005-207321) does disclose how to further improve the fuel consumption ratio.
When an alternator, which is driven by the engine, is provided in the vehicle as one of accessory devices, the fuel consumption ratio may be likewise adversely affected unless the operation of the alternator is properly controlled.